This invention pertains generally to multicolor electrographic recording devices. In particular, the present invention is a liquid toner developing module used to deposit liquid toner onto a latent electrostatic image formed on an imaging surface of a photoconductive member.
Typically, to produce a multicolor print a photoconductive member of an electrographic recording device is first charged to a uniform potential to sensitize its imaging surface. The charged surface of the photoconductive member is exposed to an image of an original document that is to be reproduced as a multicolor print. This procedure allows the photoconductive member to record an electrostatic latent image corresponding to the informational areas contained within the image of the original document.
To form a multicolor print, successive images of the original document are digitally color separated through different colored filters and recorded on the photoconductive member. These latent images are developed with different colored liquid toners supplied from corresponding toner developing modules of a toner handling network. The color of the liquid toner in a particular developing module corresponds to the subtractive primary of the color of the respective digitally separated image. Electrographic recording is normally done with yellow, cyan and magenta liquid toners. Usually the electrographic recording device also includes a developing module having black liquid toner, since it is required in virtually all commercial color printing applications. The different colored developed images are transferred from the photoconductive member to a print medium in superimposed registration with one another. Heat is usually applied to permanently fuse the image to the print medium to form a completed multicolor print.
One such liquid toner developing chamber for depositing liquid toner on an electrophotographic film is disclosed in U.S. Pat. No. 3,927,639 to Plumadore. The developing chamber includes a development electrode positioned beneath an opening in a liquid toner chamber passageway. Liquid toner is supplied through the chamber passageway opening to be deposited on an electrophotographic film placed against the opening. Liquid toner is supplied to the chamber passageway through an inlet which is coupled to a toner reservoir containing a supply of liquid toner. The toner reservoir is coupled to the inlet by a fluid line that includes a solenoid valve.
The chamber passageway further includes an outlet spaced from the inlet by the development electrode. Liquid toner that is not deposited on the electrophotographic film passes through the chamber passageway and out the developing chamber outlet. A toner vacuum separator is coupled in series with the outlet and a vacuum pump. The vacuum pump when activated, draws liquid toner from the toner reservoir through the chamber passageway to the toner vacuum separator. The toner vacuum separator separates liquid toner (that has not been deposited on the electrophotographic film and is recovered from the chamber passageway) from any air drawn into the separator from the passageway by operation of the vacuum pump. Separated toner within the toner vacuum separator is returned to the toner reservoir through a toner return line.
Air to dry the liquid toner deposited on the electrophotographic film is supplied to the chamber passageway through a conduit coupled to the developing chamber inlet. The air is drawn through the chamber passageway by operation of the vacuum pump. The vacuum pump of the developing chamber must operate at a high vacuum pressure to draw the liquid toner from the toner reservoir and through the chamber passageway to the toner vacuum separator. The high flow rate of the liquid toner through the chamber passageway may cause bubbles to form in the toner. Bubbles within the liquid toner may distort the image on the electrophotographic film since the bubbles may not allow the toner to be evenly and continuously deposited on the film. In addition, the high toner flow rate can cause the liquid toner to mist making it difficult for the toner vacuum separator to effectively and efficiently separate the undeposited toner from the air drawn in by the operation of the vacuum pump.
There is a continuing need for improved liquid toner developing modules for depositing liquid toner on an imaging surface of a photoconductive member. In particular, there is a need for a developing module that uses a low vacuum pressure to remove liquid toner from the development electrode to reduce the likelihood that bubbles will form in the liquid toner flow. The absence of bubbles will allow the toner to be evenly deposited on the photoconductive member, and thereby lessen any chance of distorting the toned electrostatic latent image on the imaging surface. In addition, there is a need for a developing module that uses a low vacuum pressure to recover undeposited toner from the development electrode to prevent the liquid toner from misting. Reduced misting allows the undeposited toner to be effectively separated from the air drawn in by the vacuum pump from around the development electrode. There is a need to simplify the toner carrying lines and valving of the developing module for efficient liquid toner handling. Moreover, there is a need for a method of aligning the development electrode of the developing module with photoconductive member that allows the liquid toner to be gradually applied to the imaging surface of the photoconductive member to ensure a high quality developed image.